Self Monitoring of Blood Glucose (SMBG) - An unnecessary burden for most diabetics?

We've all seen the TV commercials, the familiar grandfatherly actor and diabetic patient, Wilford Brimley sitting at home as he looks into the camera and encourages diabetics to "check your sugar and check it often" while he makes a cup of coffee. "Call XYZ medical supply now and get your test equipment at no cost to you" he says and then stirs in the cream and takes a sip. It sounds like a good idea doesn't it? After all its free, and obviously if you are a diabetic you want to keep your sugar under control. It would be easier to do that if you could measure your sugar level at home. In theory if you could easily check your sugar the instant feedback would tell you how your diet was working or whether the dose of your medication was correct. That's the theory, but theory and reality have a inconvenient habit of disagreeing with each other.
Home glucose monitoring machines have been available for several decades now but time and technology have made them increasingly smaller, more accurate, easier to use, and cheaper. Virtually anyone can be taught to use one of these machines at home to monitor their own sugar. Medicare as well as most insurance companies now pay for them. As these devices have become easier to obtain and operate, doctors have advised most of their diabetic patients to use them. It seemed a logical recommendation. Even today most people and many doctors believe this is good practice.

So should every diabetic check their sugars at home? The obvious answer is yes, but why would I have written this article if the obvious answer was the correct one? The correct answer is, it depends. It largely depends on whether you take insulin or not and for most type 2 diabetics who are not on insulin the correct answer may be no. Since most people with type 2 diabetes are not on insulin, the majority of diabetics may not need to monitor their blood sugar at home.

Whenever we recommend any sort of testing we always have to ask ourselves "How will this improve the patient's outcome?". The assumption with Self Monitoring of Blood Glucose (SMBG) is that a patient could use the information to improve their diet or exercise regimen. A little positive or negative feedback from these readings should over time give patients the kind of reinforcement we all respond to. A low reading after a work out would be like a pat on the back for a job well done, or if we were bad, a digital slap on the hand for the donut we knew we shouldn't have eaten.  We might also suppose that medications could be adjusted based on these readings. In general people should be able to better fine tune their diet, exercise, and medications if they knew from hour to hour what their blood sugar was at any given time.

While this idea sounds reasonable there is an alternate view and there are good reasons to believe that testing may not help in the way that we would like. The difficulty with our theory is that we are assuming there is a simple connection between what we eat or the medication we take and what our sugar will be an hour or two later. In reality its much more complicated than that.  Some of the difficulty derives from the fact that foods don't always cause blood sugar to peak at the same time. Some may cause a peak an hour later and others might peak 3 or 4 hours later. Absorption rates can also be affected by other foods that we've eaten at the same time so even the same food eaten by the same person may not always cause our blood sugar to peak the same way and at the same time. Exercise, stress, infections and many other things can affect blood sugar levels too so the same foods eaten under different circumstance may have different effects. Some of these things can be subtle and difficult to appreciate.

Its also difficult to adjust medication dose based on sugar readings. The affects of oral diabetic medications usually takes many hours to kick in and will vary from person to person in a way that is not as easy to predict as insulin. If your sugar is high in the morning its difficult to really know whether it was last night's medication dose or this morning's that was too low. If we then adjust our dose based on today's readings the effect may not show up until tomorrow and tomorrow will be a very different day.

Because of the delayed and unpredictable effect of food and oral medications it is difficult for a person to make sense of a blood sugar level. Its possible to eat a candy bar and sometimes still get a good reading or a stick of celery and find your reading is very high because the reading you take at 1pm may be affected by something you ate for breakfast or lunch or a combination of the two.  If the morning sugar is low a patient might incorrectly assume they should skip their diabetes medication that morning even though the medicine may not have its maximal effect until late in the afternoon when their sugar would have been much higher.

Now we have two different and opposite theories about whether SMBG is useful for Type 2 diabetics. Which one is the right one? Theory is fine but what we truly want to know is what happens in the real world. Fortunately this has already been examined for us in a number of trials ( see references below). Some of these studies have used a test called a HGbA1c which is done at the doctors office. HgbA1c levels are used by physicians to determine what a patients average sugar has been over the previous 90 days. This test has been used for many years to more accurately assess the effectiveness of diabetes treatments. The advantage of this test is that it smooths out the up and down spikes in blood sugar readings that occur throughout the day. In a number of studies it has been shown that maintaining a HgbA1c below 7.0 reduces the risk of diabetes associated complications.

Most studies have shown that when Type 2 diabetics on oral medications do SMBG they do not have better HgbA1c compared to patients who never check their SMBG. In at least one study the HgbA1c's were actually higher in the patients who did regular SMBG.  Additionally the use of SMBG has been found to increase psychological stress in patients.

It's not clear why this is the case but the issues mentioned above obviously play a part. It does little good to measure the effects of the last meal you ate if you don't know when those effects will actually occur. In fact measuring the SMBG might actually give someone the wrong idea. They may decide that diet really doesn't make that much of a difference since good foods sometimes resulted in higher sugars and bad foods sometimes gave them lower readings. They may also decide to skip their medication or lower the dose if their sugar reading is low when in fact that medication would not have maximally affected their blood sugar until 4 ,6, or 10 hours later. These are not just theoretical problems as I have seen these issues arise in my own patients, even in people who had been thoroughly educated in advance and warned not to do this.

Because of these issues, because of the current lack of evidence supporting any benefit from SMBG in this group of diabetics, and because of the possible harm that may come from SMBG, I do not encourage my patients to monitor their glucose at home in most cases unless they are taking insulin. I believe if we are going to ask patients to stick themselves with a sharp object daily we need good evidence that they are going to benefit from that process. Right now all the evidence says there is no benefit and there may be some harm that arises from this practice.

Of course each patient is unique and therefor anyone with questions should discuss their individual situation with their own doctor and review the risks and benefits before starting or stopping SMBG.


Michael Melgar

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